1. Field of the Invention
The present invention relates to a virtual private line control system, and more particularly to the technique for connecting and disconnecting a virtual private line using an ISDN network between private branch exchangers which have ISDN interfaces.
2. Description of the Related Art
Generally, the traffic of a telephone network changes depending upon the time zone and the day of the week. For example, in case of a telephone network system of an enterprise, the heaviest traffic tends to be during the beginning of the workday, immediately after noon, and immediately before the end of the workday. Thus, the heaviest traffic only occurs during several hours in a day.
A telephone network of an enterprise connects between the head office and each of offices, between the offices, between the head office and each of business stations, and between the business stations by private lines. Considering the high traffic hours, the enterprise contracts many telephone lines with a communication company. Therefore, some of the telephone lines are not used other than the high traffic hours. As a result, the line use efficiency decreases and the enterprise has to pay a telephone line use fee.
In order to eliminate the excessive number of private telephone lines and the excessive telephone line use fee, a virtual private line system which uses an ISDN network is proposed in Japanese Laid Open Patent Application (JP-A-Heisei 4-165892). In this reference, the number of private lines is made minimum, and virtual private lines using the ISDN network are set only for a high traffic time zone so as to increase the number of lines.
The virtual private line system adopts a time link system. In the time link system, virtual private line information is previously registered in a storage unit on the side of a station. The virtual private line information is composed of a time bit map in which the number of virtual private lines to be set with respect to route information, the number of channels, a call arrival number, a call origination number and a time zone are registered for every day and for every route. The station on the call originating side periodically searches the storage unit to read the registered virtual private line information for a present day. Then, the station refers to the time bit map to perform the setting or cancellation of the virtual private lines for a present time zone.
As described above, the conventional virtual private line system which uses the ISDN network adopts the time link system. An expected traffic is considered, and the number of virtual private lines, a connection start time of each of the virtual private lines, and a time interval are previously set in a station data. The connection of the virtual private line is realized in accordance with the station data. For this reason, even if there is not generation of any event such as a call origination at all when the virtual private line information is periodically referred to, the connecting process of the virtual private lines is performed for the number of virtual private lines set in the time zone of the time bit map. Therefore, the conventional virtual private line system is effective when the actual traffic at that time is equal to or near to the expected traffic. However, if the actual traffic at that time is lower than the expected traffic, excessive virtual private lines are connected. As a result, the improvement of the decrease of the line use efficiency and the improvement of payment of the telephone line use fee are not always enough.
Also, when events more than the expected traffic are generated, the lack of the virtual private lines occurs to cause a communication loss.
In addition the above reference, a variable communication network is described in Japanese Laid Open Patent Application (JP-A-Showa 59-127458). In this reference, a first exchanger and a second exchanger are directly connected by a first line. The first and second exchangers are connected by a second line group via one or more other exchangers. The first exchanger and each of the exchangers of a network includes a line selecting circuit for selecting an optional one of the second line group as a virtual fixed connection line. A flag field for indicating the second line group is captured for the virtual fixed connection line is provided in a signal format of a signal system between the first exchanger and each exchanger of the network. When the second line group is captured, it is set in the flag field. Thus, an optional line is captured as the virtual fixed connection line and the number of virtual fixed connection lines is adjusted based on the traffic on the first line.
A virtual private line connecting system is described in Japanese Laid Open Patent Application (JP-A-Heisei 3-125551). In this reference, private branch exchangers are connected via an ISDN network. A D channel signal circuit and a PBXxe2x80x94PBX common line signal circuit are connected to a D channel and a plurality of B channels on a user and network interface. Links by a plurality of B channels or HO channels are formed in the ISDN network by the D channel signal circuit. One of the plurality of B channels is connected to the PBXxe2x80x94PBX common line signal circuit for a virtual private line.
In addition, a virtual private line connecting system is described in Japanese Laid Open Patent Application (JP-A-Heisei 5-244250). In this reference, a call is originated from a terminal 1 to a terminal 16. When a private trunk 1 line 3 is in a communication state, an empty channel is selected and a call origination event is notified to a central control unit 8 for establishment of a virtual private lie. The central control unit 8 originates a call to an ISDN network 17 using one of numbers registered in a main storage unit 18. In a call arriving station, a central control unit 14 performs a call arriving process to a compressed speech trunk 12 which automatically responds to the ISDN network 17 via a first interface group circuit 10. The central control unit 8 connects a communication path switch of a compressed speech trunk 6 via a first interface group circuit 4. As a result, a virtual private line is established through the ISDN network 17.
Also, a communication control apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 6-181474). In this reference, when determining that a data transmission amount of an information processing apparatus par a unit time which is detected by a traffic detecting section 23 exceeds an upper limit of allowable range of data transmission amount at present, a traffic determining section 25 notifies to a packet exchange control section 24, an instruction for adding one virtual line to the same recipient. The packet exchange control section 24 sets another new virtual line between the information processing apparatus and the above recipient on an INS-P. Thereafter, the information processing apparatus performs a packet communication using the two virtual lines.
The present invention is accomplished in view of the above problems. Therefore, an object of the present invention is to provide a virtual private line control system and a method for the same, in which the connection and disconnection of a virtual private line using an ISDN network are performed in response to generation of an event such as a call origination, in a private branch exchanger which has an ISDN interface.
In order to achieve an aspect of the present invention, a private branch exchanger which is connected to an ISDN network, includes an identifying unit for identifying a specific one of a plurality of virtual private lines in response to an event, for determining whether the specific virtual private line is usable, and for issuing a communication instruction when the specific virtual private line is usable. A communication unit performs communication using a specific channel corresponding to the specific virtual private line in response to the communication instruction.
The private branch exchanger may be connected to a first terminal, and the event may be a call origination from the first terminal to a second terminal connected to another private branch exchanger which is connected to an ISDN network.
The identifying unit issues a connection instruction when a connection of the specific virtual private line to an ISDN network is not established. The private branch exchanger further comprises a connection control unit for establishing the connection of the specific virtual private line to the ISDN network in response to the connection instruction.
The connection control unit holds the specific virtual private line in a connected state for a predetermined time after the communication. In this case, the connection control unit disconnects the specific virtual private line after the predetermined time when an even using the specific virtual private line is not generated for the predetermined time.
The private branch exchanger may further include a monitoring unit monitors determines whether or not the predetermined time elapses after the communication.
In order to achieve another aspect of the present invention, a private branch exchanger which is connected to an ISDN network, includes a virtual private line information table which stores information indicating channels corresponding to virtual private lines in units of routes, an identifying unit for determining a route in response to an event, for referring to the virtual private line information table based on the determined route to determine a specific one of the channels corresponding to the virtual private lines for the determined route, for determining whether a connection of a specific virtual private line corresponding to the specific channel to an ISDN network is established, and for issuing a communication instruction when the specific channel corresponding to the specific virtual private line is usable, and a communication unit for performing communication using the specific channel corresponding to the specific virtual private line in response to the communication instruction.
The private branch exchanger may further include a virtual private line connection information table which stores connection state information indicating whether each of the plurality of virtual private lines is in a connected state or in a disconnected state, and communication state information indicating whether a channel corresponding to each of the plurality of virtual private lines is in an empty state or a communication state. In this case, the identifying unit refers to the virtual private line connection information table based on the channels corresponding to the virtual private lines for the determined route to determine whether the connection state information of each of the virtual private lines for the determined route is the connected state or the disconnected state. As a result, the identifying unit issues the communication instruction when at least one of the channels of the virtual private lines for the determined route as the specific channel has the communication state information of the empty state. Also, the identifying unit changes the communication state information for the specific channel from the empty state to the communication state.
In addition, the identifying unit issues a connection instruction, when all of the channels corresponding to some of the virtual private lines for the determined rout have the communication state information of the communication state while ones of the virtual private lines for the determined route other than the some virtual private lines have the connection state information of the disconnected state. The private branch exchanger further comprises a connection control unit for establishing the connection of one of the virtual private lines for the determined route as the specific virtual private line which has the connection state information of the disconnected state, in response to the connection instruction. The connection control unit changes the connection state information for the specific virtual private line to the connected state, and the communication state information for the specific channel corresponding to the specific virtual private line to the communication state.
The private branch exchanger may further include a monitoring unit for monitoring the channels of the virtual private lines, for changing the communication state information of the specific channel to the empty state when the communication is ended.
The virtual private line connection information table further includes a line capture time setting information indicating a time for which each of the virtual private lines should be captured after the communication is ended, and a remaining capture time information indicating a time for which the each virtual private line should be remained in a captured state. At that time, the monitoring unit sets the line capture time setting information to the remaining capture time information when the communication is ended. Also, the monitoring unit monitors the channels of the virtual private lines for every predetermined time, and updates the remaining capture time information for every channel based on the monitoring result. In addition, the monitoring unit issues a disconnection instruction when one of the virtual private lines has the remaining capture time information of 0. In this case, the connection control unit disconnects the one virtual private line having the remaining capture time information of 0.
In order to achieve still another aspect of the present invention, a method of using an ISDN network for a virtual private line, includes the steps of:
determining a route in response to an event;
referring to a virtual private line information table based on the determined route to determine the channels corresponding to the virtual private lines for the determined route the virtual private line information table storing information indicating channels corresponding to virtual private lines in units of routes;
determining a usable specific one of the channels;
issuing a communication instruction when the specific channel is determined; and
performing communication using the specific channel corresponding to the specific virtual private line in response to the communication instruction.
In this case, in order to determine a specific channel, a virtual private line connection information table is referred to based on the channels corresponding to the virtual private lines for the determined route to determine whether the connection state information of each of the virtual private lines for the determined route is the connected state or the disconnected state. The virtual private line connection information table stores connection state information indicating whether each of the plurality of virtual private lines is in a connected state or in a disconnected state, and communication state information indicating whether a channel corresponding to each of the plurality of virtual private lines is in an empty state or a communication state. As the specific channel, one of the channels having the connection state information of the connected state and having the communication state information of the empty state is determined. Also, the communication state information for the specific channel is changed from the empty state to the communication state.
The method may further includes the steps of:
issuing a connection instruction, when all of the channels corresponding to some of the virtual private lines for the determined rout have the communication state information of the communication state while ones of the virtual private lines for the determined route other than the some virtual private lines have the connection state information of the disconnected state;
establishing the connection of one of the virtual private lines for the determined route as the specific virtual private line which has the connection state information of the disconnected state, in response to the connection instruction; and
changing the connection state information to the connected state.
Also, the method may further includes the steps of:
monitoring the channels of the virtual private lines; and
changing the communication state information of the specific channel to the empty state when the communication is ended.
The virtual private line connection information table further includes a line capture time setting information indicating a time for which each of the virtual private lines should be captured after the communication is ended, and a remaining capture time information indicating a time for which the each virtual private line should be remained in a captured state. In this case, wherein the monitoring step includes setting the line capture time setting information to the remaining capture time information when the communication is ended.
Also, the monitoring step includes:
monitoring the channels of the virtual private lines for every predetermined time; and
updating the remaining capture time information for every channel based on the monitoring result.
In addition, the method may further include the steps of:
issuing a disconnection instruction when one of the virtual private lines has the remaining capture time information of 0; and
disconnecting the one virtual private line having the remaining capture time information of 0.